A power of appointment is “imperative” where the creating instrument manifests an intent that the permissible appointees be benefited even if the donee fails to exercise the power. An imperative power can exist even though the donee has the privilege of selecting some and excluding others of the designated permissible appointees. All other powers of appointment are “discretionary.” The donee of a discretionary power is privileged to exercise, or not to exercise, the power as the donee chooses.